This application claims the priority benefit of Taiwan application serial no. 88114312, filed Aug. 21, 1999, the full disclosure of which is incorporated herein by reference.
1. Field of the Invention
The invention relates in general to a chemical mechanical polisher. More particularly, this invention relates to a composite polishing pad used in a chemical mechanical polisher.
2. Description of the Related Art
Surface planarization is a very important technique that directly affects the precision of a photolithography process. Only when the surface is planarized, a scattering effect of the exposure light can be avoided to transfer a pattern with fidelity.
Currently, two planarization techniques including spin-on-glass (SOG) and chemical mechanical polishing (CMP) have been widely used in industry. As the semiconductor fabrication technique has approached the deep sub-micron regime, the required level of planarity can not be achieved using the technique of spin-on-glass. The only technique to provide the required level of planarity in a very large scale integration (VLSI) or ultra large scale integration (ULSI) is chemical mechanical polishing. In the chemical mechanical polishing process, a polishing theory similar to that used for a grinder is used with the aid of a chemical reagent. The uneven surface profile is thus smoothed. With an appropriate control of the polishing parameters, about 90% of planarity can be achieved using chemical mechanical polishing.
FIG. 1A and FIG. 1B are a top view and a cross sectional view of a conventional chemical mechanical polisher. The chemical mechanical polisher comprises a turning table 10, a polishing pad 13 on the turning pad, a top ring 11 for retaining a wafer 12 for polish, a transportation tube 14 for slurry 19 supplying and a pump 15 for providing the slurry 19.
While performing a chemical mechanical polishing step, the turning pad 10 and the top ring 11 are rotating along a certain direction, for example, the direction indicated by the arrow 18a and 18b. The slurry is continuously supplied onto the polishing pad 13 for polishing. Being held by the top ring 11, the wafer 12 has a surface to be polished in contact with the polishing pad 13, the uneven parts of the surface to be polishing is thus planarized with the aid of the slurry 19.
The parameters to affect the effect of planarization for a chemical mechanical polishing step includes the structure and material of the polishing pad, the material of the slurry and the rotating speed of the turning table and the top ring. A structure of a conventional polishing pad is shown as FIG. 2A. The turning table and the polishing pad are contacted with each other. The polishing pad 25 includes a lower polishing pad 24 in contact with a turning table 22 and an upper polishing pad 26 on the lower polishing pad 24. The lower and the upper polishing pads 24 and 26 are in a circular shape with a same size that is slightly larger than the size of the turning table 22.
FIG. 2A to FIG. 2C shows an initiating step for a polishing pad to illustrate how the structure of the polishing pad affects the polishing. An unworked polishing pad 25 is shown as FIG. 2A, while the upper polishing pad 26 has a surface with a poor roughness that cannot perform the polishing step. Thus, as shown in FIG. 2B, a dresser (conditioner) 28 is used to initiate the upper polishing pad 26 to effectively achieve the polishing effect with the aid of the slurry. In addition, after the polishing pad has been used for once, the polishing pad is inevitably consumed to fail to meet the polishing requirement. The initiating step is required to perform on the polishing pad again.
The polishing pad 25 is typically designed with a larger radius than that of the turning table 22, so that the polishing pad 25 can be renewed easily. As a consequence, the initiating effect is only resulted on the part supported by the turning table 22. As shown in the figure, the part experienced with a direct pressure of the dresser 28 is dished, while the rim 30 of the polishing pad 25 raises relatively. A hollow part 29 is thus formed as shown in FIG. 2C. While performing polishing on the initiated polishing pad 25, the used slurry or polishing particle thus cannot be discharged to seriously affect the polishing effect.
To resolve the problem for discharging the used slurry or polishing particles, the projecting rim 30 is cut away, typically by notching 32 at a point from the hollow part 29 of the polishing pad 25. While cutting the projecting rim 30, the polisher has to be opened. Meanwhile, a great possibility of contamination is caused, and numbers of particles or defects on product are thus increased to decrease the yield of product. Moreover, the usage of the polishing pad is so frequent and the renewal rate is high. If a cutting step is required while initiating each polishing pad, the consuming time is more than half an hour. Therefore, a long time and a great effort of labor are consumed. Moreover, the operator for performing the initiating step has to be well trained. If the cutting skill is poor, problems such as unintentionally hooking the wafer retained by the top ring or wafer dropped from the top ring occur while the polishing pad is cut into too small a piece. Or the underlying material is contaminated if a notch is cut too deep.
The invention provides a composite polishing pad used in a chemical mechanical polisher. The composite polishing pad comprises an upper polishing pad and a lower polishing pad which is concentrically disposed on a turning table. The lower polishing pad has a diameter the same as that of the turning pad. Therefore, the lower polishing pad and the turning pad are overlapped with each other thoroughly. The lower polishing pad has a handler on a periphery thereof for a convenient renewal. The upper polishing pad is disposed on the lower polishing pad concentrically. The upper polishing pad has a diameter between a covering range of a dress for initiating the composite polishing pad and a covering range of a top ring for retaining a wafer to be polished.
By designing the upper polishing pad with a diameter between the dresser of the composite polishing pad and the covering range of the top ring, the formation of the projecting portion in the conventional structure is eliminated. The manually cutting or notching step is skipped. The problems the induced thereby can thus be resolved. Moreover, the design of the handler enables an operator to renew the polishing pad without opening the polisher. Thus, the contamination can be further eliminated, and the time consuming for the renewal can be shortened.
The structure of the composite polishing pad can be modified into a lamination of a lower polishing pad slight larger than the turning table and an upper polishing pad with having size between the covering ranges of the dresser and the top ring. In this manner, the composite polishing pad can be easily renewed without the formation of a handler.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.